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Hello,
After building 2 labsubs in the early years i never forget
the impact of a hornloaded design, with all the dynamics it had.
This time i have to build a subwoofer for a home theater room and
would like to go back to the hornloaded approached.
The design has to be a special horn that can be placed in the corner, what already have some benefits.
I was wondering or anyone has some experience with it and how low can the in room response be made flat with eq?
gr. Marcel
Follow Ups:
I once looked up "room gain" and found some good articles and discussion at the data-bass website.
The short version (as others, like Geddes, have noted) is that the room effects will make ANY speaker non smooth in the bass. Using more sources helps even it out - by a substantial amount. Room gain is real, but is only smooth and predictable below 10Hz.
Are you free to modify the room itself (manifolds, wall treatment etc)?
Not much is going on in most recordings at 10Hz.
Dave
Below the horn's cutoff the system reverts to being a sealed box (assuming the back of the driver is sealed). So you can model and EQ it the same way you can a sealed box. It just depends on how much power, power handling and excursion you have to work with as to how low you can get it to go for a certain output level.
I know in my room I get a +10dB shelf below about 40Hz that almost exactly compensates for my sealed sub's rolloff. I figured this out by doing basically what you suggest - measuring outside, then inside. Although really at low frequencies, I was just measuring inside to see what EQ I needed to apply. But knowing the room gain did tell me how much output I could get at the listening position relative to the max output I measured outside.
They are shaped like a triangle.....sorry couldn't resist
E
T
> The design has to be a special horn that can be placed in the corner
Any horn can be placed in a corner. You'll get 1/8 space loading so long as the mouth is less than 1/4 wavelength from the three boundaries. You may build the horn along the lines of the KHorn, which in effect made two of the room walls part of the enclosure, but you don't have to. As alluded to by Tom in-room response can actually go lower than the horn corner frequency when cabin gain is factored into the equation.
you just described a Klipsch LaScala, which depends on it.
Generally a horn can be equalized down to the low cutoff (FC).
The FC is determined by the horn's path length and flare rate, generally the path length is 1/4 the wavelength of the lowest frequency that can be effectively reproduced. As an example a 30 Hz FC would require a 9.4 foot path length, the corner can be part of the path length.
Under certain circumstances you can EQ a little below Fc, but I've found that it takes a well-designed bass horn with closed box back volume behind the woofers to do it--not vented.
For instance, the Klipsch Jubilee bass bin will easily load to flat response down to 32 Hz from its nominal 40 Hz Fc by adding one PEQ boost filter. The increase in distortion is typically much less than adding TH or even typical front-loaded horn subwoofers. The added LF response has been popular among those owners that do not own or employ horn-loaded subwoofers.
Chris
"As far as the ear can tell, consistently clean and spacious bass can be reproduced only by a driver unit coupled to a horn-type acoustic transformer..."; Jack Dinsdale, May 1974
Hi
In a normal room there is a room gain slope which can be from +12dB per octave in a sealed concrete bunker to more like +3 to +9 dB per octave in a normal house.
This (with a flat a flat response speaker in half space or outdoors) produces a rising response once one is below the lowest room mode which is often associated with the 1/2 wavelength frequency of the largest room dimension.
In an automobile where this effect is easier to see, one can take a sealed box which rolls off around 50Hz at -12dB/oct and when you place it in the car, you can (with windows rolled up) get flat response down an octave or a lot more below the normal corner due to the room gain or cabin gain slope as they often call it in the auto world.
In a sealed car, the +12dB cabin gain slope cancels out the -12dB slope from the speakers roll LF off, perhaps the closest thing to a free lunch in audio
Hope that helps
Tom Danley
Danley Sound Labs
So, since a sealed back horn (including a lab sub) eventually has a -12dB /oct roll off, one might figure out approximately where your lowest room mode would be and then shoot for a horn that has a response knee around that same point.
Hi thnx all for the reply.
I also read, from archived post, that the corner has also
a hornloading effect an the radiator.
Would it be possible to extract the adding resistive and reactance load of a measurements and intergrate this in my model, for the last final flare?
I had a tought about measuring a simple sealed radiator outside (free from reflection) and then measuring it in the room, placing the radiator where the mouth off the horn would normally be.
The difference in resistive and reactance load would be presenting the extra hornloading of the corner. I dont know it this would be represantative.
I want to come as close as possible to the 20hz corner.
gr. Marcel
My listening room has a concrete floor and long wall. The room is also thickly paneled on all 4 walls. The volume setting on my subwoofer tells me that their is a lot off room gain. Very satisfying base is achieved at a very low volume setting in relation to the satellites.
Dave
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